Automatic development control

ABSTRACT

An apparatus for regulating the developability of a multi-color developing system utilized in a reproducing machine. The regulating apparatus controls image density and maintains color balance. Environmentally induced developabillity changes and toner colorant usage rate variations are adjusted by controlling the concentration of selected toner colorants in the corresponding developer material. The foregoing abstract is neither intended to define the invention disclosed in the specification, nor is it intended to be limiting as the scope of the invention in any way.

United States Patent 1191 Whited [111 3,754,821 [451 Aug. 28,1973

AUTOMATIC DEVELOPMENT CONTROL Charles A. Whited, Fairport, N.Y;

Assignee: Xerox Corporation, Stamford,

Conn.

Filed: Dec. 28, 1971 Appl. No.: 213,056

Inventor:

[52] US. CL... 355/4, 250/227, 355/17 356/176 Int. Cl 603g 15/00 Field of Search 355/3 DD, 4, l7;

[56] References Cited UNITED STATES PATENTS 9/1969 Johnson 355/4 8/l97l Dybvig et al 355/4 2/l972 Egnaczak et al 355/4 X Primary Examiner-Samuel S. Matthews Assistant Examiner-Richard A. Wintercorn Attorney- 15m J. Ralabate, Henry Fleischer, et a1 [5 7 ABSTRACT An apparatus for regulating the developability of a multi-color developing system utilized in a reproducing machine. The regulating apparatus controls image density and maintains color balance. Environmentally in duced developabillity changes and toner colorant usage rate variations are adjusted by controlling the concentration of selected toner colorants in the corresponding developer material.

The foregoing abstract is neither intended to define the invention disclosed in the specification, nor is it intended to be limiting as the scope of the invention in any way.

24 Claims, 8 Drawing Figures Patented Aug. 23, 1973 3,754,821

5 Sheets- Sheet 1 Patented Aug. 28, 1973 3 Sheets-Sheet 2 1 AUTOMATIC DEVELOPMENT CONTROL BACKGROUND OF THE INVENTION This invention relates generallyto an apparatus for regulating the developability of a multi-color developing system, and more particularly concerns an appara tus which controls the image density and color balance during the formation of a multi-color copy by an electrostatic reproducing apparatus.

Developability, as pertains to an electrostatic reproducing machine, can be defined as'the ability of the developer material used therein to develop an image to a specified density. A developability regulating apparatus adjusts the characteritics of the developing material to produce developed images on a copy which have a suitable density and color balance.

Developability is related to the concentration of toner colorants in the developer material, i.e., the percentage of toner colorants relative to carrier granules in the developer mixture. Environmental conditions such as temperature and humidity conditions affect developability. The physical parameters of the developing system also'affect developability, e.g., spacing, electrical bias, mass flow rate, and magnetic field pattern, amongst others. In addition, many other factors such as the state of compaction of the developer material, the electrical charges on the toner colorants and the carrier granules as well as the state of attraction of toner colorants to the carrier granule surface influence developability. For example, two batches of substantially identical developer material may have the same concentration of toner colorants, however, one batch located in a low humidity environment will produce a multi-color color copy having an image density and color balance that is different from a copy produced by another batch locatedin a high humidity environment. The regulating approach, pursuant to the present invention, is to control toner colorant concentration within the developer material to maintain image density and color balance.

Previously numerous other systems have been devised to add toner to the developer mixture. However, these systems are concerned with black and white reproduction rather than multi-color reproduction. One such system is described in US. Pat. No. 3,399,652 issued to Gawron on Sept. 3, 1968. This patent discloses a rotating reflective disc located directly in the developer mix. The disc'is electrically biased to attract toner from the mix; The amount of toner attracted to the surface of the disc is a function of the concentration of toner in the mix. A light beam is reflected from the surface of the disc onto a photoelectric unit. The intensity of the light striking the photoelectric unit is a measure of the density of toner adhering to the disc surface. The

' photoelectric unit is calibrated to initiate a signal to a dispensing apparatus for replenishing the supply of toner in the developer mix when the density of toner adhering to the disc surface, as measured by the intenthe quality of .the developed image. Further more, whereas the apparatus disclosed in the Gawron patent controls the concentration of a single toner colorant used to form a black and white copy, the present invention'relates to an apparatus which regulates a plurality of tone colorants to provide appropriate image density and color balance on a multi-color copy.

Accordingly, it is an object of the present invention I to improve the developability of a multi-color copy by regulating developed image density and color balance.

SUMMARY OF THE INVENTION Briefly stated, and in accordance with the present invention, there-is provided an apparatus which regulates the developability of a multi-color developing system. The regulating apparatus detects the density of a simulated image and controls the respective concentration of toner colorant in the developer material to maintain a quality image having satisfactory color balance.

In accordance with the present invention, the apparatus includes a transparent electrode positioned to pass through the developer material. While in the development zone, an electrical voltage having a magnitude sufficient to simulate the latent electrostatic image recorded on the photoconductive member is placed on the electrode to attract toner colorant thereto. The

electrode is illuminated and sensingmeans detect the intensity of the light rays passing therethrough'. An electrical output signal indicative of the density of toner colorant deposited on the electrode is produced by the sensing-means. Comparing means develop a control signal corresponding to the deviation between the output signal and a reference. .T he control signal represents the variationrbetween the actual density of the selected toner colorant 'deposited on the electrode and the desired density thereof. Dispensing means, actuated by the control signal, furnish additional toner colorant from the respective toner container to the developing system to adjust developability to provide satisfactory image density'and' color balance on the copy.

BRIEF DESCRIPTION OF THE DRAWINGS ings, in which:

FIG. I is a schematic perspective view of an automatic electrostatic reproducing machine embodying the features of the present invention;

FIG. 2 is a sectional elevational view of the photoconductive drum used in the reproducing machineil lustrated in FIG. 1 and showing, in detail, the apparatus of the present invention for regulating the developability of a multi-color developing system;

FIG. 3 is a sectional elevational view of the assembly used to conduct biasing voltage and light rays to the transparent electrode of the FIG. 2 regulating apparatus; I

FIG. 4 is a sectional elevational view depicting the transparent electrode used in the present invention;

FIG. 5a schematically illustrates biasing the transparent electrode with a voltage simulating the latent electrostatic image recorded on the photoconductive drum;

FIG. 5b schematically illustrates the deposition of toner colorant on the transparent electrode;

FIG. '50 schematically depicts light rays. passing through the transparent electrode having toner colorant deposited thereon and the intensity thereof being detected by the photosensor; and 1 FIG. 5d schematically shows the transparent electrode being cleaned by a brush cleaner in preparation for the next cycle after the biasing voltage has been removed therefrom.

While the present invention will be described in connection with a preferred embodiment and method associated therewith, it will be understood that it is not intended to limit that invention to that embodiment and method. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THEINVENTION With continued reference to the drawings wherein like reference numerals have been used throughout to designate like elements, FIG. 1 schematically illustrates an automatic electrostatic reproducing machine for producing multi-color copies from a color signal. The reproducing machine depicted therein employs a photoconductive member, such as rotatably mounted drum 10, having a photoconductive surface 12 thereon. Photoconductive surface '12, preferably, is formed of a material having a relatively panchromatic response to white light. Drum rotates in the direction indicated by arrow 14 to move photoconductive surface 12 sequentially through a series of processing stations. First, drum surface 12 passes through charging station A which has positioned therein a corona generating device, indicated generally at 16, extending transversely across drum surface 12. Corona generating device 16 charges drum surface 12 to a relatively high uniform potential.

The charged drum surface 12 is next rotated to exposure station B which includes a moving lens system, generally designated by the reference numeral 18, and a color filter mechanism, shown generally at 20. An original 22 is stationarily supported upon a transparent viewing platen 24 wherein successive incremental areas of the original are illuminated by means of a moving lamp assembly shown generally at 26. Lens system 18 is adapted to'scan successive areas of illumination at platen 24 and to focus the light on photoconductive drum surface 12. Lamp assembly 26 and lens system 18 are moved in a timed relation with the drum surface '12 to produce a flowing light image of the original on photoconductive surface 12 of drum 10 in a non-distorted manner. During exposure, filter mechanism 20 interposes selected color filters in the optical light path of lens 18. The color filters operate on the light passing through the lens to record a latent electrostatic image on the photoconductive surface corresponding to a specific color of the flowing light image of the original.

Subsequent to the recording of latent electrostatic image on drum surface 12, drum 10 is rotated to development station C which includes three individual developer units generally indicated by the reference numerals 28, 30 and 32. The developer units are all of a type generally referred to in the art as magnetic brush development units. Typically, in a magnetic brush development system, magnetizable developer material including carrier granules and toner colorants is continually brought through a directional flux field and a brush of developer material is formed. Developer particles are continually moving so as to provide the brush consis'tently with fresh developer material. Development is achieved by bringing the brush into contact with photoconductive surface 12. Each of the development units 28, 30 and 32, respectively, apply a toner colorant corresponding to the compliment of the specific color separated latent electrostatic image recorded on the photoconductive surface, each toner. colorant being adapted to absorb light within a preselected spectral region of the electromagnetic wave spectrum corresponding to the wavelength of light transmitted through the filter.-

In accordance with the present invention, additional toner colorants are added to the developer material when developability, as hereinbefore described, is re duced deleteriously. The regulating apparatus, indicated generally at 34, includes a transparent electrode assembly 36mounted on photoconductive surface 12 of drum l0. Illuminating means, such as light source 38, in cooperation with fiber optics 40 transmit light rays through transparent electrode assembly 36. During development, toner colorants are deposited on the transparent electrode and the intensity of the light rays passing therethrough is indicative of the density thereof. Sensing means, such as photosensor 42, is adapted to receive the light rays transmitted through transparent electrode assembly 36 and develop an electrical output signal corresponding to the intensity of the rays. Comparing means, e.g., suitable analog and reference circuitry, compares the electrical output signal from photosensor 42 to a reference signal and generates a logic control signal for dispensing a selected toner colorant into the corresponding developer unit.

After development, the now visible images are moved sequentially to transfer station D where the images are transferred to a sheet of final support material by means of a biased transfer roll shown generally at 44. Thesurface of transfer roll 44 is electrically biased to a potential having a magnitude and polarity sufficient to electrostatically attract toner colorant from the photoconductive surface 12 of drum 10 to final support sheet 45. A single sheet of final support material is supported on the transfer roll and the roll arranged to move in synchronism with photoconductive surface 12 so that each of the developed images is placed in superimposed registration upon sheet 45. g

A suitable recess in the biased transfer roll prevents the transparent electrode from contacting the transfer roll. In this way, the toner colorant deposited on the transparent electrode is not disturbed by the transfer process and presents a true indication of developabil- After the last transfer operation, support sheet 45 is stripped from the roll surface and passed to a fusing sta-' tion (not shown) where the transferred image is fixed to support sheet 45. Thereafter, sheet 45 is advanced to the catch tray (not shown) for subsequent removal by an operator.

The last processing station in the direction of drum rotation, as indicated by arrow 14, is cleaning station E. A rotatably mounted fibrous brush 47 is positioned in cleaning station E and is maintained in contact with photoconductive surface 12 of rotating drum l0 and transparent electrode assembly 36 to remove residual toner colorants remaining thereon after the transfer operation.

The process employed in the reproducing machine is a subtractive color-to-color reproducing process wherein toner colorants containing the subtractive primaries yellow, cyan and magenta are employed to provide the wide range of colors found in the original on the copy. The first step in producing a color copy is to ascertain the color composition of the original subject matter and record this information on photoconductive surface 12 of drum 10. The color original is. optically scanned at number of times to formulate successive latent electrostatic images on photoconductive surface 12. Each light image is passed through a color filter to form a color separated latent electrostatic image. The latent image formed by passing the light image through a filter is developed by a complementary toner colorant as areas of relatively high charge density on photoconductive surface 12 indicate the absence of the filtered light while areas of relatively low density on photoconductive surface 12 indicate the presence of the filtered light in the colored original. For example, a latent image formed by passing the light image through a green filter will record the magentas as areas of relatively high charge density on photoconductive surface 12 while the green light rays will cause the charge density on photoconductive surface 12 to be reduced to an ineffective development level. The magentas are then made visible by simply applying a green absorbing masembly 36 is sensed by photosensor 42. The output signal from photosensor 42 is processed by suitable logic elements and, depending upon the density of toner colorant deposited on the electrode, toner colorant may or may not be added to the respective developer unit. Photosensor 42 is mounted exterior to the photoconductive surface 12 of drum 10 and positioned to sense the density of toner colorant deposited on transparent electroodeassembly 36 just prior to clearing photoconductive surface 12 of drum l0, i.e., before drum 10 is rotated tocleaning station E since electroode assembly 36 undergoes a regular photoconductive drum cleaning process. Light source 38 may be inside drum 10 or, as shown in FIG. 2, external to the drum with the light rays'conducted therein by means of fiber optics 40. Shaft 46, supporting drum 10, is a tubular member and permits fiber optics 40 to pass through the hollow cengenta toner colorant to the latent image recorded on photoconductive surface 12. Similarly, a blue separation is developed with a cyan toner colorant. The three developed, color separated images are then brought together in registration on a sheet of final support material to produce a multi-color copy corresponding to the multi-color original.

Turning now to FIG. 2, there is shown the detailed construction of regulating apparatus 34. Regulating apparatus 34 includes a transparent electrode assembly 36, a light source 38, fiber optics 40, a photosensor 42 and suitable logic means for-processing the electrical output signal. In addition each of the developing units 28, and 32, respectively, have a corresponding toner container associated therewith. Each toner container houses a supply of selected toner colorants to form a reservoir of the selected'toner colorants for the appropriate developer unit. For example, the toner container of developer unit 28 houses cyan toner, developer unit 30 magenta toner, and developer unit 32 yellow toner. Dispensing means, snch as perforations within the containe'r, are adapted to meter out a specified quantity of a selected 'toner colorant to the appropriate developer unit. A suitable vibrator oscillates theappropriate container to shear the toner colorant and thereby dispense it through the perforations in the container to the corresponding developer. Regulating apparatus 34 controls the dispensing of toner colorants from the toner container to the respective developing unit.

simulating the latent electrostatic image on the photoconductive surface 12 of drum 10. Preferably, the electrode is biased about 200 volts above developer bias, normal developer bias being about 500 volts. However, the electrode may be biased from about 100 volts to about 600 volts above the developer bias. The density of the image developed on transparent electrode astral core thereof and out therefrom to photoconductive surface 12 .to direct light rays from light source 38 to transparent electrode assembly 36.

In order to apply the appropriate voltage corresponding to the latent electrostatic image deposited on the drum, transparent electroode assembly 36 must be biased to a suitable voltage level. This is achieved, preferably, by mounting a commutator assembly, indicated generally at 48, in the region of the end bell of drum 10. A suitable slip ring assembly may be used in lieu of commutator assembly 48. Timing for the application of ,the bias voltage to electrode assembly 36 may be controlled by alternating means such as suitable electronic switching why use of a split commutator ring, i.e., the electrode being biased over one portion of the commutator and not over the remaining portion. The bias voltage is removed from the transparent electrode during the cleaning process. In lieu of applying a bias voltage to electroode assembly 36, a suitable bias may be applied thereto by electrical charging.

if a single photosensor is used the aging characteristics of light source 38 are .critical and should be maintained relatively stable. However, if a pair of photosensors are utilized in a wheatstone-bridge type of arrangement the aging characteristics of light source 38 are not critical. 7

Light source 38 is preferably a derated tungsten lamp with a regulated voltage, e.g., a 7 volt tungsten filament lamp operating from a 5 volt source.

Photosensor 42 is a commercially available silicon phototransistor such as produced by the General Electric Company, Model No. L148. This device has some response to the visible portion of the spectrum, but the peak response isin the region of the near infrared. This will not cause any significant problem since the toner colorant deposited on electroode assembly 36 acts as a light defuser rather than as a color filter. Photosensor 42 is maintained in a controlled thermal environment to minimize the effects of its temperature sensitivity. Oven 106 maintains the thermal environment at 50 1 1C, or ,atany appropriate temperature suitable for photosensor 42.

Directing means,such as fiber optics 40, transmit the light rays emitted from light source 38 to transparent electrode assembly 36. The light rays are transmitted through transparent electrode assembly 36 and the intensity thereof is measured by photosensor 42. Preferably, glass fiber optics are used to obtain good transmittance in the near infrared region. Glass fiber optics do not attenuate radiant energy inthe most sensitive region of the silicon phototransistor which isthe preferred photosensor. As shown in FIG. 2, fiber optics 40 extends from light source 38 through the core of drum shaft 46 to a suitable fiber optic connector 41 and radially outwardly therefrom to photoconductive surface 12, where it is secured to transparent electrode 36. In this way, light rays are transmitted from light source 38 to electrode 36.

Suitable logic elements process the electrical output signal from photosensor 42. The logic elements, preferably include a suitable discriminator circuit for cor'nparing a reference with the electrical output signal from photosensor 42. The discriminating circuit may utilize a silicon control switch which turns on and effectively locks in after an electrical output signal has been obtained having a magnitude greater than the reference level (i.e., set point). The signal from the discriminator circuit changes the state of a flip-flop to develop an output signal therefrom. The output signal from the flip-flop, in conjunction with an output signal from the appropriate developer unit actuate an AND gage which, in turn, transmits a control signal to the dispensing means within the toner container housing the toner colorant corresponding to the developer unit generating the output signal to the AND gate The control sig nal also rests the flip-flop. The type of logic circuit heretofore disclosed is on-off. However, in the altemative, it is possible to utilize proportional circuitry which varies the quantity of toner colorant metered to the respective developer units as a function of the magnitude of the control signal. This may be achieved by a suitable integrated circuit module for developing a stepped proportional dispensing rate.

Duplicate logic elements are utilized for each developer unit, i.e., yellow developer unit, cyan developer unit and magenta developer unit. Hence, there are three separate, independent logic channels, each channel being associated with its respective developer unit. The density of toner colorant deposited on the surface of photoconductive surface 12 is a function of the concentration of toner colorant within the developer material. The concentration of toner colorant is, in turn, a function of the magnitude of the reference signal. Thus, by adjuting the respective references image density as well as color balance is regulated. I

Referring now to FIG. 3, there is shown a sectional view of the commutator assembly 48. A segmented commutator 52 is mounted on a plastic housing 54. Commutator 52 is segmented so that transparent electroode assembly 36 is biased to the appropriate level when passing through the development zone. This is achieved by the utilization of a spring loaded pin 56 which delivers power to the commutator ring which in turn transmits the power to transparent electroode assembly 36. A bracket 60 is mounted to plastic housing 58 to prevent the rotation thereof when plastic housing 54 rotates with photoconductive drum 10. Lead 62 conducts power from the segmented commutator 52 to transparent electode assembly 36. Seal 64, preferably made from an elastomeric material, rotates with the drum shaft and forms a dust-tight seal to prevent particles from contaminating the segmented commutator and light path interface. Turning once again to FIG. 2, electrical connector 45 engages spring loaded contact 43 to conduct the biasing voltage from lead 62 to lead 63 for applying a biasing voltage to electrode 36.

Referring now to FIG. 4, there is shown a sectional view of transparent electrode assembly 36. Transparent electroode assembly 36 includes a glass window 66 having a transparent tin oxidecoating. This type of transparent, electrically conductive glass is made by Pittsburgh Plate Glass under the trademark NESA or is made by the Coming Glass Company under the trademark Electro Conductive. Electrically conductive glass 66 is mounted on a brass conductor 68 and is biased to the appropriate voltage level equivalent to the latent electrostatic image recorded on photoconductive surface 12 of drum l0 (FIG.2). Brass conductor 68, having electrically conductive glass 66 mounted slidably therein, is in turn, secured to an elastomeric insulating material such as glass filled nylon which is indicated by reference numeral 70. Spacer 72 positions lens 74 with respect to conductive glass 66. In a similar manner, spacer 78 locates lens 76 directly behind lens 74 so that the pair of lenses focus the light rays passing through fiber optics 40. The entire assembly is resiliently mounted in brass conductor 68 by means of a suitable coil spring 87. Spacer ring 84, in association with clamping ring 86, securely locks the entire assembly hereinbefore described together. Furthermore, clamp 86 is in engagement with the lower end portion of brass conductor 68 and includes thereon a mounting bracket 88 for securing lead wire 62 thereto in order to provide a biasing voltage for electrically conductive glass 66. Insulating ring includes a threaded portion 70a integral with the lower end thereof which is in threaded engagement with grooved clamping ring 90. Spacer ring 92 is interposed between the upper surface of clamping ring and the interior surface of drum 10 to position clamping ring 90 relative thereto. Glass 66 is secured in position in the wall of drum I0 by means of a pivotable retaining ring 94 associated with a helical spring 96. Spring 96 is mounted on flange 86a of clamp 86. The opposed end portion of spring 96 is in engagement with flange 94a which extends radially inwardly and is integral with retaining ring 94. In this manner, latch 94b is pivoted to a closed position to engage clamping ring 90 so as to resiliently urge the glass 66 into position within the mounting hole on photoconductive drum 10.

Turning again to FIG. 2, the light passing through glass window 66 is transmitted to photosensor 42 by fiber optics 98. Fiber optics 98 are mounted in plenum chamber 100 by suitable mounting means such as clamp 102. Positive laminar air flow is directed into the chamber as indicated by arrow 104 to purge the system and reduce toner colorant deposition. Fiber optics 98 extend into over 106 and pass through a heat-tight aperture therein to conduct light rays transmitted through electrode assembly 36 to photosensor 42 mounted therein. Photosensor 42 and the associate circuit elements are all mounted within oven 106 and are maintained at a temperature of 50 1C. In this way the temperature sensitivity of photosensor 42 does not influence the performance of the regulating apparatus.

Referring now to FIGS. 5a through 5d inclusive, there is shown the sequence of events required to requlate image density and maintain color balance. In FIG. 5a, voltage is applied to transparent electrode assembly 36. The voltage applied thereto preferably simulates the latent electrostatic image recorded on photoconductive surface 12. This voltage is automatically applied to the transparent electrode assembly 36 via the position of the segmented commutator 52 as hereinbefore discussed. Thus, just prior to entering the development zone a voltage of about 200 volts above developer bias is appliedto transparent electrode assembly 36. As

drum 10 rotates into the developer zone, as indicated in FIG. b, the magnetic brush assembly of the respective developer unit applies toner colorants to transparent electrode assembly 36. Toner colorants are attracted to transparent electrode assembly 36 by the voltage differential of approximately 200 volts between transparent electrode assembly 36and the respective developer unit. In FIG. 50, drum has rotated to a position wherein electroode assembly 36 is aligned with fiber optics 98 to transmit the light passing therethrough to photosensor 42. This in turn, produces an electrical output signal which is compared by the circuitry with the reference to develop-a control signal for actuating the dispenser in the appropriate toner container housing the selected toner colorant. As shown in FIG. 5d, the biasing voltage is removed from transparent electrode assembly 36, i.e., the split commutator ringrotates to an open circuit position in which transparent electrode 36 is not biased and thereafter brush 47 at cleaning station E'removes toner colorants adhering to the surface of electrode 36. The aforementioned procedure is repeated three successive times for each copy produced, i.e., it is repeated for each of the toner colorants (cyan, magenta, yellow) in the system.

Hence, the regulating apparatus of the presentinvention improves the developability of a multi-color copy sity of toner colorant deposited on said electrode means and the desired density thereof; and means, actuatedby the control signal, for dispensing the selected toner colorant into the developing system to achieve the requisite system developability.

3. Apparatus as recited in claim 2, further including logic means for actuating the appropriate comparing means correpsonding to the toner colorant undergoing development.

'4. Apparatus as recited in claim 1, further including means for adjusting the reference level to achieve a color balance for successive toner colorants being de posited on said electrode means.

5. Apparatus as recited in claim 1, wherein said illuminating means includes:

a light source; and

means for directing light rays from said light source through said electrode means having toner colorant deposited thereon.

6. Apparatus as recited in claim 5, wherein said sensing means includes a photosensor positioned in light receiving relation with said directing means to receive the light rays passingthrough the toner colorant deposited on said electrode means.

7. Apparatus as recited in claim 1, further including means, associated with said electrode means, for cyclicly alternating the electrical charge on said electrode to attract toner colorant thereto during the developby controlling the concentration of toner colorants within the developer material in response to the density of toner colorant deposited on a simulated latent electrostatic image. In this manner, the regulating apparatus insures that the image density and color balance of the mu'lti-color copy are repeatedly of a high quality.

It is therefore apparent that there has been provided, in accordance withthe invention, an apparatus for regulating the developability of a developing system that fully satisfies the objects, aims and advantages set forth 7 above. While thisinvention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.

What is claimed is: 1. Apparatus for regulating the developability of a multi-color developing system adapted to utilize a plurality of developer materials having selected toner colorants capable of absorbing light energy within a preselected spectral region, including:

transparent electrode means electrically biased to attract toner colorant thereto as said electrode means passes through the developer material;

means for illuminating said electrode means having toner colorant deposited thereon with light rays; and

means for sensing the intensity of the light rays transmitted through said electrode means to produce an electrical output signal indicative of the density of toner colorant deposited thereon.

2. Apparatus as recited in claim 1, further including means for comparing the electrical output signal with a reference level to produce a control signal corresponding to the deviation between the actual denment thereof and to repel toner colorant therefrom after the intensity of light rays transmitted through said electrode means has been detected by said sensing means.

8. A method of regulating the developability of a multi-color developing system adapted to use a plurality of developer materials having selected toner colorants capable of absorbing light energy within a preselected spectral region, including the steps of:

placing an electrical charge on a transparent electrode; passing the electrode through the developer material to attract toner colorant thereto for developing the electrode;

illuminating the electrode having toner colorant deposited thereon; and

sensing the intensity of the light rays transmitted through the electrode to produce an electrical output signal indicative of the'density of toner colorant deposited thereon. 4 I 9. A method as recited in claim 8, further including the steps of:

comparing the electrical output signal with a reference level to produce a control signal corresponding to the deviation between the actual density of toner colorant deposited on the electrode and the desired density thereof; and

dispensing'the selected toner colorant into the developer material to achieve the requisite system developability.

10. A method as'recited in claim 9, further including the steps of:

cleaning thefirst mentioned toner colorant deposited on the electrode therefrom after the electrical charge thereon has been removed;

placing a second electrical charge on the transparent electrode,

passing the transparent electrode through a second developer material to attract a second toner colorant thereto for developing the electrode;

illuminating the electrode having the second toner colorant deposited thereon; and sensing the intensity of the light rays passing through the electrode having the second toner colorant deposited thereon to produce a second electrical output signal indicative of the density of the second toner colorant. 11. A method as recited in claim 10, further including the steps of:

comparing the second electrical output signal with a second reference level to produce a second control signal corresponding to the deviation between the actual density of the second toner colorant deposited on the electrode and the desired density thereof; and

dispensing the second toner colorant into the secon developer material to achieve the requisite system developability.

12. A method as recited in claim 11, further including the steps of adjusting the second reference level relative to the first mentioned reference level to attain the desired color balance between the first mentioned toner colorant and the second toner colorant.

13. A method as recited in claim 8, wherein said step of illuminating the electrode includes directing light rays through the electrode having toner colorant deposited thereon.

14. A method as recited in claim 8, further including the step of cyclically alternating the electrical charge on the electrode to attract toner colorant thereto during the development thereof and to repel toner colorant therefrom after the intensity of light rays transmitted throgh the electrode has been detected.

15. Apparatus for regulating the developability of an electrostatic reproducing machine of the type having a photoconductive member and developing system utilizing a developer material having toner colorants adapted to be deposited on a latent electrostatic image recorded on the photoconductive member to produce a colored powder toner image thereon, including:

transparent electrode means mounted on the photoconductive member and electrically biased to attract toner colorant thereto as the photoconductive member passes through the developer material; and

means for illuminating said electrode means having toner colorant deposited thereon with light rays;.

and

means for sensing the intensity of the light rays transmitted through said electrode means to produce an electrical output signal indicative of the density of toner'colorant deposited thereon.

16. Apparatus as recited in claim 15, further including:

means for comparing the electrical output signal with reference level to produce a control signal corresponding to the deviation between the actual density of toner colorant deposited on said electrode means and the desired density thereof; and

means, actuated by the control signal, for dispensing toner colorant into the developing system to achieve the requisite system developability.

17. Apparatus as recited in claim 15, wherein said illuminating means includes:

a light source; and means for directing light rays from said light source through said electrode means having toner colorant deposited thereon.

18. Apparatus as recited in claim 17 wherein said sensing means includes a photosensor positioned in light receiving relation with said directing means to receive the light rays transmitted through the toner colorant deposited on said electrode means.

19. Apparatus as recited in claim 15, further including means, associated with said electrode means for cyclically alternating the electrical charge on said electrode means to attract toner colorant thereto during the development thereof and to repel toner colorant therefrom after the intensity of light rays transmitted through said electrode means has been detected by said sensing means.

'20. A method of regulating the developability of an electrostatic reproducing machine of the type having a photoconductive member and developing system utilizing a developer material having toner colorants adapted to be deposited on a latent electrostatic image recorded on the photoconductive member to produce a colored powder toner image thereon, including the steps of:

placing an electrical charge on a transparent electrode mounted on the photoconductive member;

passing the photoconductive member with the electrode through the developer material to attract toner colorant thereto;

illuminating the electrode having toner colorant deposited thereon;

sensing the intensity of the light rays transmitted through the electrode to produce an electrical output signal indicative of the density of toner colorant deposited thereon.

21. A method as recited in claim 20, further including the steps of:

comparing the electrical output signal with a reference level to produce a control signal corresponding to the deviation between the actualdensity of toner colorant deposited on the electrode and the desired density thereof; and

dispensing toner colorant into the developer material to achieve the requisite system developability.

22. A method as recited in claim 21, further including the steps of:

cyclically alternating the electrical charge on the electrode to attract toner colorant thereto during the development thereof and to repel toner colorant therefrom after the intensity of light rays passing through the electrode has been detected; and cleaning the toner colorant deposited on the electrode therefrom after the electrical charge thereon has been removed.

23. A method as recited in claim 21, further including the step of adjusting the reference level to attain the desired image density by selecting the appropriate concentration of toner colorant within the developer material.

24. A method as recited in claim 20, wherein said step of illuminating the electrode includes directing light rays through the electrode having toner colorant deposited thereon. 

1. Apparatus for regulating the developability of a multi-color developing system adapted to utilize a plurality of developer materials having selected toner colorants capable of absorbing light energy within a preselected spectral region, including: transParent electrode means electrically biased to attract toner colorant thereto as said electrode means passes through the developer material; means for illuminating said electrode means having toner colorant deposited thereon with light rays; and means for sensing the intensity of the light rays transmitted through said electrode means to produce an electrical output signal indicative of the density of toner colorant deposited thereon.
 2. Apparatus as recited in claim 1, further including means for comparing the electrical output signal with a reference level to produce a control signal corresponding to the deviation between the actual density of toner colorant deposited on said electrode means and the desired density thereof; and means, actuated by the control signal, for dispensing the selected toner colorant into the developing system to achieve the requisite system developability.
 3. Apparatus as recited in claim 2, further including logic means for actuating the appropriate comparing means correpsonding to the toner colorant undergoing development.
 4. Apparatus as recited in claim 1, further including means for adjusting the reference level to achieve a color balance for successive toner colorants being deposited on said electrode means.
 5. Apparatus as recited in claim 1, wherein said illuminating means includes: a light source; and means for directing light rays from said light source through said electrode means having toner colorant deposited thereon.
 6. Apparatus as recited in claim 5, wherein said sensing means includes a photosensor positioned in light receiving relation with said directing means to receive the light rays passing through the toner colorant deposited on said electrode means.
 7. Apparatus as recited in claim 1, further including means, associated with said electrode means, for cyclicly alternating the electrical charge on said electrode to attract toner colorant thereto during the development thereof and to repel toner colorant therefrom after the intensity of light rays transmitted through said electrode means has been detected by said sensing means.
 8. A method of regulating the developability of a multi-color developing system adapted to use a plurality of developer materials having selected toner colorants capable of absorbing light energy within a preselected spectral region, including the steps of: placing an electrical charge on a transparent electrode; passing the electrode through the developer material to attract toner colorant thereto for developing the electrode; illuminating the electrode having toner colorant deposited thereon; and sensing the intensity of the light rays transmitted through the electrode to produce an electrical output signal indicative of the density of toner colorant deposited thereon.
 9. A method as recited in claim 8, further including the steps of: comparing the electrical output signal with a reference level to produce a control signal corresponding to the deviation between the actual density of toner colorant deposited on the electrode and the desired density thereof; and dispensing the selected toner colorant into the developer material to achieve the requisite system developability.
 10. A method as recited in claim 9, further including the steps of: cleaning the first mentioned toner colorant deposited on the electrode therefrom after the electrical charge thereon has been removed; placing a second electrical charge on the transparent electrode, passing the transparent electrode through a second developer material to attract a second toner colorant thereto for developing the electrode; illuminating the electrode having the second toner colorant deposited thereon; and sensing the intensity of the light rays passing through the electrode having the second toner colorant deposited thereon to produce a second electrical output signal indicative of the density of the second toner colorant.
 11. A method As recited in claim 10, further including the steps of: comparing the second electrical output signal with a second reference level to produce a second control signal corresponding to the deviation between the actual density of the second toner colorant deposited on the electrode and the desired density thereof; and dispensing the second toner colorant into the second developer material to achieve the requisite system developability.
 12. A method as recited in claim 11, further including the steps of adjusting the second reference level relative to the first mentioned reference level to attain the desired color balance between the first mentioned toner colorant and the second toner colorant.
 13. A method as recited in claim 8, wherein said step of illuminating the electrode includes directing light rays through the electrode having toner colorant deposited thereon.
 14. A method as recited in claim 8, further including the step of cyclically alternating the electrical charge on the electrode to attract toner colorant thereto during the development thereof and to repel toner colorant therefrom after the intensity of light rays transmitted throgh the electrode has been detected.
 15. Apparatus for regulating the developability of an electrostatic reproducing machine of the type having a photoconductive member and developing system utilizing a developer material having toner colorants adapted to be deposited on a latent electrostatic image recorded on the photoconductive member to produce a colored powder toner image thereon, including: transparent electrode means mounted on the photoconductive member and electrically biased to attract toner colorant thereto as the photoconductive member passes through the developer material; and means for illuminating said electrode means having toner colorant deposited thereon with light rays; and means for sensing the intensity of the light rays transmitted through said electrode means to produce an electrical output signal indicative of the density of toner colorant deposited thereon.
 16. Apparatus as recited in claim 15, further including: means for comparing the electrical output signal with reference level to produce a control signal corresponding to the deviation between the actual density of toner colorant deposited on said electrode means and the desired density thereof; and means, actuated by the control signal, for dispensing toner colorant into the developing system to achieve the requisite system developability.
 17. Apparatus as recited in claim 15, wherein said illuminating means includes: a light source; and means for directing light rays from said light source through said electrode means having toner colorant deposited thereon.
 18. Apparatus as recited in claim 17 wherein said sensing means includes a photosensor positioned in light receiving relation with said directing means to receive the light rays transmitted through the toner colorant deposited on said electrode means.
 19. Apparatus as recited in claim 15, further including means, associated with said electrode means for cyclically alternating the electrical charge on said electrode means to attract toner colorant thereto during the development thereof and to repel toner colorant therefrom after the intensity of light rays transmitted through said electrode means has been detected by said sensing means.
 20. A method of regulating the developability of an electrostatic reproducing machine of the type having a photoconductive member and developing system utilizing a developer material having toner colorants adapted to be deposited on a latent electrostatic image recorded on the photoconductive member to produce a colored powder toner image thereon, including the steps of: placing an electrical charge on a transparent electrode mounted on the photoconductive member; passing the photoconductive member with the electrode through the developer material to attract toner colorant thereto; ILLUMINATING the electrode having toner colorant deposited thereon; sensing the intensity of the light rays transmitted through the electrode to produce an electrical output signal indicative of the density of toner colorant deposited thereon.
 21. A method as recited in claim 20, further including the steps of: comparing the electrical output signal with a reference level to produce a control signal corresponding to the deviation between the actual density of toner colorant deposited on the electrode and the desired density thereof; and dispensing toner colorant into the developer material to achieve the requisite system developability.
 22. A method as recited in claim 21, further including the steps of: cyclically alternating the electrical charge on the electrode to attract toner colorant thereto during the development thereof and to repel toner colorant therefrom after the intensity of light rays passing through the electrode has been detected; and cleaning the toner colorant deposited on the electrode therefrom after the electrical charge thereon has been removed.
 23. A method as recited in claim 21, further including the step of adjusting the reference level to attain the desired image density by selecting the appropriate concentration of toner colorant within the developer material.
 24. A method as recited in claim 20, wherein said step of illuminating the electrode includes directing light rays through the electrode having toner colorant deposited thereon. 